Speed optimized trajectory control for motor vehicles

ABSTRACT

A trailer backup assist system for motor vehicles includes an auxiliary user input feature that can be used by a vehicle operator to provide a steering curvature command corresponding to a desired vehicle path curvature without requiring a user to move a steering wheel of the motor vehicle. The trailer backup assist system is configured to control a vehicle speed while the vehicle is backing up with a trailer attached thereto utilizing an input comprising at least one of a steering curvature command and an angle of a trailer relative to the vehicle. The trailer backup assist system controls at least one of a brake system, an engine torque, and a transmission gear selection to thereby control vehicle speed in a reverse direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to U.S. patent application Ser. No.14/256,427, which was filed on Apr. 18, 2014, now U.S. Pat. No.9,493,187, issued on Nov. 15, 2016, entitled “CONTROL FOR TRAILER BACKUPASSIST SYSTEM” which is a continuation-in-part of U.S. patentapplication Ser. No. 14/249,781, which was filed on Apr. 10, 2014, nowU.S. Pat. No. 9,374,562, issued on Jun. 21, 2016, entitled “SYSTEM ANDMETHOD FOR CALCULATING A HORIZONTAL CAMERA TO TARGET DISTANCE,” which isa continuation-in-part of U.S. patent application Ser. No. 14/243,530,which was filed on Apr. 2, 2014, now U.S. Pat. No. 9,513,103, issued onDec. 6, 2016, entitled “HITCH ANGLE SENSOR ASSEMBLY,” which is acontinuation-in-part of U.S. patent application Ser. No. 14/201,130,which was filed on Mar. 7, 2014, now U.S. Pat. No. 9,290,202, issued onMar. 22, 2016, entitled “SYSTEM AND METHOD OF CALIBRATING A TRAILERBACKUP ASSIST SYSTEM,” which is a continuation-in-part of U.S. patentapplication Ser. No. 14/188,213, which was filed on Feb. 24, 2014, nowabandoned, entitled “SENSOR SYSTEM AND METHOD FOR MONITORING TRAILERHITCH ANGLE,” which is a continuation-in-part of U.S. patent applicationSer. No. 13/847,508, which was filed on Mar. 20, 2013, now abandoned,entitled “HITCH ANGLE ESTIMATION.” U.S. patent application Ser. No.14/188,213 is also a continuation-in-part of co-pending U.S. patentapplication Ser. No. 14/161,832, which was filed on Jan. 23, 2014, nowU.S. Pat. No. 9,346,396, issued on May 24, 2016, entitled “SUPPLEMENTALVEHICLE LIGHTING SYSTEM FOR VISION BASED TARGET DETECTION,” which is acontinuation-in-part of U.S. patent application Ser. No. 14/068,387,which was filed on Oct. 31, 2013, now U.S. Pat. No. 9,102,271, issued onAug. 11, 2015, entitled “TRAILER MONITORING SYSTEM AND METHOD,” which isa continuation-in-part of U.S. patent application Ser. No. 14/059,835,which was filed on Oct. 22, 2013, now U.S. Pat. No. 9,248,858, issued onFeb. 2, 2016, entitled “TRAILER BACKUP ASSIST SYSTEM,” which is acontinuation-in-part of U.S. patent application Ser. No. 13/443,743which was filed on Apr. 10, 2012, now U.S. Pat. No. 8,825,328, issued onSep. 2, 2014, entitled “DETECTION OF AND COUNTERMEASURES FOR JACKKNIFEENABLING CONDITIONS DURING TRAILER BACKUP ASSIST,” which is acontinuation-in-part of U.S. patent application Ser. No. 13/336,060,which was filed on Dec. 23, 2011, now. U.S. Pat. No. 8,909,426, issuedon Dec. 9, 2014, entitled “TRAILER PATH CURVATURE CONTROL FOR TRAILERBACKUP ASSIST,” which claims benefit from U.S. Provisional PatentApplication No. 61/477,132, which was filed on Apr. 19, 2011, entitled“TRAILER BACKUP ASSIST CURVATURE CONTROL.” The aforementioned relatedapplications are hereby incorporated by reference in their entirety. Theabove-identified patents and patent applications may be collectivelyreferred to herein as “The Related Patents and Patent Applications.”

FIELD OF THE INVENTION

The present invention generally relates to systems forcontrolling/assisting vehicles during backup operations, and inparticular to a system that controls vehicle speed during parking ortrailer backup operations.

BACKGROUND OF THE INVENTION

Backing up a vehicle with a trailer can be a difficult task. Inconventional motor vehicles, the operator must control the steering andvehicle speed while the vehicle is moving in reverse. Trailer backupassist systems have been developed to assist operators when backing up avehicle having a trailer attached thereto.

Motor vehicles may also include active park assist systems that assist adriver during vehicle parking operations. Such systems may be configuredto provide automated parking. During parking operations, the vehicle maybe moved in a reverse direction.

The path that a vehicle is capable of following in reverse is limited bythe design of the vehicle and trailer (if present), and road conditions.Furthermore, the path that a vehicle (and trailer) is capable of in areverse direction may be more limited at higher vehicle speeds.

SUMMARY OF THE INVENTION

One aspect of the present invention is a trailer backup assist systemfor motor vehicles. The trailer backup assist system includes anauxiliary user input feature that can be used by a vehicle operator toprovide a steering curvature command corresponding to a desired vehiclepath curvature without requiring a user to move a steering wheel of themotor vehicle. The trailer backup assist system is configured to controla vehicle speed while the vehicle is backing up with a trailer attachedthereto utilizing an input comprising at least one of a steeringcurvature command and an angle of a trailer relative to the vehicle. Thetrailer backup assist system generates a command to control at least oneof a brake system, an engine torque, and a transmission gear selectionto thereby control vehicle speed in a reverse direction based, at leastin part, on the steering curvature command and/or the angle of a trailerrelative to the vehicle.

Another aspect of the present invention is a method of controlling aspeed of a motor vehicle in a reverse direction when a trailer isconnected to the motor vehicle. The method includes utilizing at leastone of a trailer angle and a steering curvature command from anauxiliary user input feature positioned in a vehicle interior as acontrol input. The method further includes controlling vehicle speed ina reverse direction based at least in part on the control input.

Another aspect of the present invention is a method of controlling aspeed of a motor vehicle when the motor vehicle is traveling in areverse direction. The method includes determining a desired vehiclepath in a reverse direction based at least in part on a steeringcommand. The method also includes determining an acceptable errorcriteria relative to the desired vehicle path. A speed of the vehicle islimited by controlling at least one of a vehicle brake, an enginetorque, and an automatic gear selection such that the vehicle is capableof moving in a reverse direction along the desired vehicle path withinthe acceptable error criteria.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view of a motor vehicle including a trailer backupassist system according to one aspect of the present invention;

FIG. 2 is a fragmentary view of a portion of a vehicle interiorincluding an auxiliary steering input that can be utilized by a vehicleoperator when the vehicle is backing up with a trailer attached thereto;

FIG. 3 is a graph showing a steering angle as a function of time.

FIG. 4 is a schematic plan view of a motor vehicle and a trailer atvarious positions along a vehicle path; and

FIG. 5 is a graph showing maximum allowable vehicle speed versus trailerangle; and

FIG. 6 is a partially schematic plan view showing a vehicle parkingoperation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the invention as oriented in FIG. 4. However, itis to be understood that the invention may assume various alternativeorientations and step sequences, except where expressly specified to thecontrary. It is also to be understood that the specific devices andprocesses illustrated in the attached drawings, and described in thefollowing specification, are simply exemplary embodiments of theinventive concepts defined in the appended claims. Hence, specificdimensions and other physical characteristics relating to theembodiments disclosed herein are not to be considered as limiting,unless the claims expressly state otherwise.

With reference to FIG. 1, a motor vehicle 1 according to one aspect ofthe present invention includes a trailer backup assist system 2 that canbe utilized by a vehicle operator to assist the operator when the motorvehicle 1 is backing up with a trailer 10 attached thereto. The trailerbackup assist system 2 includes a trailer backup steering inputapparatus 4 that is operably connected to a trailer back-up assistcontrol module 6. The trailer backup assist system 2 further includes ahitch angle detection apparatus 8 that is operably connected to thetrailer back-up assist control module 6.

The trailer back-up assist control module 6 is operably connected to abrake system control module 12 and a power system control module 14. Thevehicle 1 also includes a power steering assist system 16 including apower steering assist control module 18 and a steering angle detectionapparatus 20. The power steering assist control module 18 is operablyconnected to the trailer backup assist control module 6. Trailer 10 mayinclude a hitch angle detection component 22 that is operably connectedto the hitch angle detection apparatus 8 of vehicle 1. Hitch angledetection component 22 is configured to measure the angle of trailer 10relative to vehicle 1 about a vertical axis. A trailer angle of zerogenerally corresponds to an operating condition wherein the trailer 10is aligned with vehicle 1 such that the vehicle 1 and trailer 10 movealong a straight path. Hitch angle detection component 22 may also beconfigured to measure an orientation of trailer 10 relative to vehicle 1about a first horizontal axis that extends side-to-side, and a secondhorizontal axis that extends in a vehicle fore-aft direction. Thisenables the trailer backup assist system 2 to determine if trailer 10has begun to move up a slope and/or if trailer 10 has twisted relativeto vehicle 1 due to moving onto a surface that is sloped to the side. Itwill be understood that various hitch angle detection/measuring devicesmay be utilized, and the components may be mounted on vehicle 1, ontrailer 10, or on both. The vehicle 1, trailer backup assist system 2,trailer 10, and related components of FIG. 1 are described in detail inThe Related Patents and Patent Applications, such that these componentswill not be described in detail herein.

Vehicle 1 may also include an active park assist system 30 to provideautomated or assisted vehicle parking. The active park assist system 30may be operably connected to one or more of the trailer backup assistsystem 2, trailer backup steering input apparatus 4, trailer backupassist control module 6, hitch angle detection apparatus 8, trailer 10,brake system control module 12, power train system control module 14 andpower steering assist system 16, power steering assist control module18, and steering angle detection apparatus 20. As discussed in moredetail below in connection with FIG. 4, the active park assist system 30may be utilized by a vehicle operator during vehicle parking operationseither with or without a trailer 10 being connected to vehicle 1.

With further reference to FIG. 2, an auxiliary user input such as arotatable knob 25 may be mounted to a vehicle interior component such asa center console 26. Upon activation of the trailer backup assist system2, a user can rotate knob 25 to provide a user steering request to thepower steering assist system 16. During vehicle backup operations, auser can utilize the knob 25 to provide steering input rather thanrotating the vehicle steering wheel. More specifically, the angularposition of the rotatable knob 25 may correlate to a desired curvature,such that rotation of the knob 25 to a different angular positionprovides a different desired curvature with an incremental change basedon the amount of rotation. As discussed in more detail below, thetrailer backup assist system 2 and/or the active park assist system maybe configured to generate steering command signals to change the wheelangle of the steered wheels. The steering command signals may bedirectly proportional to the user steering request, or the system mayoverride or modify the steering request to generate steering commandsignals. The rotatable knob 25 may be biased (e.g., by a spring return)to a center or at-rest position P(AR) between opposing rotational rangesof motion R(R), R(L). In the illustrated embodiment, a first one of theopposing rotational ranges of motion R(R) is substantially equal to asecond one of the opposing rotational ranges of motion R(L), R(R). Toprovide a tactile indication of an amount of rotation of the rotatableknob 25, a force that biases the knob toward the at-rest position P(AR)can increase (e.g., non-linearly) as a function of the amount ofrotation of the rotatable knob 25 with respect to the at-rest positionP(AR). Additionally, the rotatable knob 25 can be configured withposition indicating detents such that the driver can positively feel theat-rest position P(AR) and feel the ends of the opposing rotationalranges of motion R(L), R(R) approaching (e.g., soft end stops). Theauxiliary user input knob 25 and operation thereof is described indetail in The Related Patents and Patent Applications (e.g. U.S. PatentPublication No. 2014/0343793), such that a detailed description of thisaspect of the trailer backup assist system 2 is not included herein.

With further reference to FIG. 3, a steering angle (“pinion angle”)versus time for a motor vehicle 1 may include a lag between a controllersteering request/command (line 34) and the actual or “absolute” steeringangle (line 36). Specifically, if a steering request or command isgenerated at a time t=0.0 as designated 32 in FIG. 3, a pinion anglecommand (line 34) is input into the power steering assist system 16.However, due to the time lag in the system, the absolute steering anglefollows the dashed line designated 36 in FIG. 3. This results in adeviation angle Δθ whereby the absolute pinion angle 36 is less than thecommand 34. In the illustrated example, the Request Ramp Time (RRT) is0.8 seconds. After 0.8 seconds, the pinion angle request line 34transitions to a horizontal line segment 34 a. After 1.0 seconds theabsolute steering angle 36 reaches a transition point 38, andtransitions to a horizontal line segment 36 a. This defines a maximumdelay “DT” of 0.2 seconds. In the illustrated example, the horizontalline segment 36 a is spaced below line segment 34 a to define a maximumstatic deviation (“MSD”) of about 2.0°. The upwardly curved line segment36 b represents an “overshoot” of the absolute steering angle 36 thatmay be as great as 2.0° relative to the horizontal static steering angle36 a. In the illustrated example, the pinion angle request 34 acorresponds to a pinion angle of 400°. The angle of the steered wheels(typically the front wheels) of a vehicle relative to the pinion angleof FIG. 3 varies depending on the gear ratios in the steering system,and the relationship between the pinion angle and the wheel angle may benonlinear. In the illustrated example, the pinion angle 400° correspondsto a wheel angle of about 22°. It will be understood that FIG. 3illustrates a typical steering response. However, the actual dynamic andstatic variations of the steering angle relative to a steering commandangle will vary from vehicle-to-vehicle. As discussed in more detailbelow, the trailer backup assist system 2 (FIG. 1) and/or the activepark assist system 30 may be configured to take into account thesteering angle time lag and steering angle variations illustrated inFIG. 3 to determine steering angle commands based on steering wheelangle requests and vehicle operating parameters.

With further reference to FIG. 4, a vehicle 1 and trailer 10 move alonga path 40 as they back up. The path 40 may include a portion 40A havinga smaller radius, and a portion 40B that is substantially straight, orhas a very large radius. The trailer angle is zero when path 40 isstraight, and increases as the radius of the path portion 40A decreases.Thus, the trailer angle between vehicle 1 and trailer 10 will be greaterin the path portions 40A than the relatively straight path portions 40B.The trailer backup assist system 2 may be configured to limit the speedof vehicle 1 and trailer 10 during backup to a maximum speed. Forexample, when the operator actuates the trailer backup assist system andutilizes the auxiliary user input knob 25 (FIG. 2), the trailer backupassist system 2 may limit the speed of vehicle 1 to 10 mph, even whenthe trailer angle is zero degrees and the vehicle 1 and trailer 10 aremoving along a straight portion 40B of path 40. However, according toone aspect of the present invention, if the vehicle 1 and trailer 10 arefollowing a portion 40A of path 40 having a relatively small radius ofcurvature, the speed of the vehicle 10 may be limited by the trailerbackup assist system 2 to a speed that is less than 10 mph to ensurethat control is maintained and to avoid jackknifing.

The trailer backup assist system 2 may be configured to limit vehiclespeeds in reverse when a trailer 10 is attached to vehicle 1 to ensurethat vehicle 1 can be controlled and to prevent jackknifing or otherproblematic operating conditions. FIG. 5 illustrates various ways to mapmaximum allowable vehicle speed as a function of trailer angle. In use,the trailer angle can be measured while the vehicle 1 is backing up, andthe trailer backup assist system 2 limits the vehicle speed using, forexample, the vehicle brakes or drivetrain such that the vehicle 1 doesnot exceed the maximum allowable speed even if a vehicle operatorattempts to back up at a higher speed by depressing the acceleratorpedal. With further reference to FIG. 5, line 42 represents a maximumallowable vehicle speed at different trailer angles. In the illustratedexample, the line 42 is a straight line, and the maximum vehicle speedat a trailer angle of 0° is 10 mph, and the maximum allowable vehiclespeed is reduced to 0 at a trailer angle of 90°. It will be understoodthat the maximum vehicle speed may be reduced to 0 at a lower trailerangle (e.g. 60°) as shown by the line 44. Also, as shown by the line 46,the maximum vehicle speed may not be limited to speed that is below 10mph until a trailer angle of significantly greater than 0° (e.g. 30°) isreached, and the maximum vehicle speed may then be limited by a straightline that goes to 0 at a predefined trailer angle (e.g. 60°). In FIG. 5,the line 46 includes a segment 46 a that is horizontal until the trailerangle reaches 30°, and the maximum allowable vehicle speed thentransitions linearly to 0 as shown by the line segment 46 b. The maximumallowable vehicle speed as a function of the trailer angle may also benon-linear (e.g. parabolic) as shown by the dashed lines 44 and 50.

The maximum allowable vehicle speed for a given trailer angle may bedetermined empirically to provide a plurality of pairs of data points,and the data may be interpolated utilizing a curve fit to therebygenerate a line representing the maximum allowable vehicle speed as afunction of the trailer angle. Alternatively, the maximum allowablevehicle speed as a function of a trailer angle may be modeled utilizinga straight (linear) line of the form y=mx+b, or a curved (nonlinear)line of the form y=mx²+cx+b, or other suitable equation.

The trailer backup assist system 2 and/or active park assist system 30may also take into account other variables to determine the maximumallowable vehicle speed for a given operating condition. For example,the curves illustrated in FIG. 5 may be modified to account for hillangles. Specifically, if the vehicle 1 and trailer 10 are backing up ahill, the maximum allowable vehicle speed may be reduced for a given(measured) trailer angle. The hill angle may be measured utilizing agravity sensor on board vehicle 1, or it may be measured utilizing asensor in hitch 52 (FIG. 4) interconnecting vehicle 1 and trailer 10.Additional variables such as road conditions may also be utilized toadjust the maximum allowable vehicle speed at a given trailer angle. Forexample, the vehicle 1 may include sensors that enable the trailerbackup assist system to determine if the vehicle is on loose gravel, wetpavement, or other surface having reduced fraction. If the vehicle 1and/or trailer 10 are on a gravel or wet surface, the maximum allowablevehicle speed for a given trailer angle may be further reduced to ensurethat the operator can maintain control of the trailer 10 during thebackup operations.

Also, the hill angle may be determined utilizing topographicalinformation that may be stored by the trailer backup assist system 2 orobtained utilizing a GPS system. Vehicle 1 may include an electroniccompass or other device whereby the location and orientation of vehicle1 on a topographical map may be determined, such that the hill angle ofthe vehicle 1 and trailer 10 can be determined.

Also, road condition data can be obtained from a remote source, and themaximum allowable vehicle speed can be adjusted if required. Forexample, if weather data in the vicinity of vehicle 1 indicates that itis raining or snowing, the maximum allowable vehicle speed for a given(measured) trailer angle may be reduced to account for the decrease intraction. Similarly, map data concerning the road surface (e.g. gravelor paved road) may be utilized to adjust the maximum allowable vehiclespeed as a function of trailer angle.

In operation, a user actuates the trailer backup assist system 2, andbegins to back up the vehicle 1 and trailer 10. The user utilizes theauxiliary user input knob 25 to provide steering requests to the trailerbackup assist system 2. The trailer backup assist system 2 utilizesvehicle speed and trailer angle data to determine a maximum allowablevehicle speed, taking into account road conditions and the like asdiscussed above.

In general, the trailer backup assist system 2 can ensure that thevehicle 1 and trailer 10 do not exceed the maximum vehicle speed versustrailer angle criteria of FIG. 5 by limiting the speed of the vehicle,limiting the trailer angle, or both. Limiting the vehicle speed can beaccomplished by sending a command to the brake system control module 12and/or the power train system control module 14. The brake systemcontrol module 12 can be utilized to apply the brakes of the vehicleand/or the brakes of a trailer 10 if the trailer 10 is equipped withbrakes. Also, the power train control module 14 can be utilized to limitthe amount of torque generated by the vehicle's engine and/or by downshifting the engine transmission to utilize engine braking if thevehicle 1 has an internal combustion engine. If the vehicle 1 has anelectric motor, the powertrain system control module may utilize theelectric motor to provide braking. The trailer backup assist system 2may also be configured to increase the vehicle speed if the vehiclespeed and trailer angle are within the allowable limits.

The trailer backup assist system 2 may also be configured to control theangle of the steering wheels to ensure that the vehicle speed versustrailer angle (FIG. 5) does not exceed the allowable limits. In thiscase, the trailer backup assist system 2 will limit the angle of thesteered wheels to a level that is lower than the input request by theuser utilizing the knob 25 (FIG. 2) to prevent the trailer angle fromexceeding the allowable limits for a given vehicle speed. Thus, thetrailer backup assist system 2 may “override” a user steering requestand generate a steering command that comprises a reduced steering anglerelative to the user steering request. For example, if the vehicle 1 istraveling in reverse at 10 mph, and an operator rapidly rotates the knob25, the trailer backup assist system 2 may apply the brakes to slow thevehicle, but the capability of the system may not allow the speed of thevehicle to be reduced quickly enough to permit the vehicle to follow thesteering input by the user. In this case, the trailer backup assistsystem 2 may generate a steering command to the power steering systemthat is reduced to avoid unacceptable operating conditions (i.e. tootight of a turn for the vehicle speed). Also, if vehicle 1 is travelingat a very slow speed (e.g. 1.0 mph), the trailer angle is still limiteddue to the physical constraints of the interface between the vehicle 1and trailer 10. Thus, the trailer backup assist system 2 may beconfigured to modify user steering requests and to limit the commands tothe power steering system to a maximum value that may be less than aninput request by a user utilizing the knob 25.

Furthermore, trailer backup assist system 2 may be configured toprioritize the user-requested steering input from knob 25 over thevehicle speed when determining whether to limit the vehicle speed orlimit the turn angle to avoid the maximum allowable values as shown inFIG. 5. In general, the input provided by a user to the knob 25corresponds to a desired vehicle path (e.g. vehicle path 40; FIG. 4),and the trailer backup assist system 2 may be configured to assume thatthe desired path is more important than the desired speed. Thus, thetrailer backup assist system 2 may be configured to first adjust thevehicle speed to stay within the maximum allowable vehicle speed shownin FIG. 5, followed by (in terms of priority) limiting the steeringangle if required to stay within the allowable limits shown in FIG. 5.

Also, as discussed above in connection with FIG. 3, the actual steeringangle may lag the steering angle request, and the final (static)steering angle may be somewhat less than the steering request. Thetrailer backup assist system 2 may be configured to optimize the vehiclespeed in reverse to follow the desired path 40 (FIG. 4) within anacceptable error. This allows the system to keep the steering speedwithin an optimum range to help keep the vehicle 1 on the desired path40 with an acceptable amount of error. In general, the required speed ofthe steering system is a function of the vehicle speed and the lateralmovement needed to follow the desired path 40. For example, the steeringspeeds required to follow a particular lateral change in path increasewith vehicle speed. Likewise, the steering speeds required at aparticular vehicle speed increase as the change in lateral movementincreases.

Vehicle speed may also be controlled during parking operations if thevehicle 1 is on a sloped surface. As shown in FIG. 6, a vehicle 60 (withno trailer attached) may be parked utilizing the active park assistsystem 30. In general, vehicle 60 is initially travelling adjacentparked cars 62 and 64, and the vehicle 60 is initially spaced apart fromthe parked cars 62 and 64 by a distance “PD.” After the vehicle 60passes a parking space 66 between parked vehicles 62 and 64, the activepark assist system 30 is actuated by the operator, and the vehicle 60travels in a reverse direction along a path shown by arrows 68. Theparking space 66 is generally rectangular, and has a slot depth “SD” anda slot length “SL.” The active park assist system 30 may be configuredto limit vehicle speed based on road conditions (e.g. gravel) and/or thehill angle (e.g. topographical map data) that is encountered by vehicle60.

The steering lag shown in FIG. 3 can be utilized by the trailer backupassist system 2 when a vehicle 1 is backing up with a trailer 10 (FIG.4), and when a vehicle 60 without a trailer is being parked (FIG. 6). Ineither case, the trailer backup assist system 2 or the active parkassist system 30 determine a desired vehicle path based on a user inpututilizing knob 25 (FIG. 2) or based on a calculated path determined byactive park assist system 30.

In general, the vehicle speed and steering can be controlled to optimizethe vehicle path in any combination. For example, the power train systemcontrol module 14 (FIG. 1) may be controlled to control the torqueoutput. The torque output can be monitored and modified to help maintainthe optimum speed to support the capability of the steering system toposition the vehicle on a desired path. The power train torque outputmay be limited to reduce the speed of the vehicle when needed by thesteering system to keep the vehicle path error within a desirable range.Similarly, the brake torque generated may also be monitored and modifiedto help maintain the optimum speed to support the capability of thesteering system to position the vehicle on a desired path. The brakesystem control module 12 may be actuated to reduce the speed of thevehicle when needed by the steering system to keep the path error withina desirable range. Furthermore, the automatic gear selection of thevehicle may be controlled, and the vehicle may down shift to facilitateengine braking and reduce the risk of overheating the braking system.Still further, if the vehicle is backing up with a trailer attached, andif the trailer has trailer brakes, the trailer brake torque may bemonitored and modified to help maintain the optimum speed to support thecapability of the steering system to position the vehicle on a desiredpath. The trailer brake torque may be applied to help reduce the speedof the vehicle when needed by the steering system to keep the path errorwithin a desirable range.

In addition to the automated control discussed above, the vehicle mayalso include a warning system that alerts a user when the vehicle speedand/or steering angle are excessive, such that the desired path cannotbe achieved by the vehicle. For example, the vehicle 1 may include avisual display (not shown), or the vehicle may be operably connected toan operator's smart device such as a cell phone or tablet. Anilluminated camera display, heads up display, illuminated mirrors (text)or schematic screen displays may be used with a variety of color,intensity, and blank frequencies to provide feedback to the driver thata collision mitigation function is active and/or to help guide thedriver to avoid the collision. The vehicle may also be configured toprovide audible tones or voice commands utilizing speakers in thevehicle and/or a driver's smart device (e.g. cell phone) to instruct thedriver how to avoid a collision, or to inform the driver that anautomated collision mitigation function is active. Still further, asteering wheel torque and/or vibration may be utilized to help a driveravoid a collision or to inform the driver that an automated collisionmitigation function is active. Other subsystems or devices such asphones, tablets, vibrating seats, or the like may also be used to warn adriver. The frequency of the vibration can be changed to conveyadditional information about the probability of the collision.

Numerous communication/warning arrangements may be utilized to conveyinformation to the driver. Such devices may include, without limitation,the vehicle audio system, park aid speakers, text display, navigationsystem, reverse camera system, messaging seats, joystick, a steeringwheel, mirrors, a mobile phone, a mobile computing device, and/or amobile gaming device.

It will be understood that the vehicle may be configured to utilize thespeed and trajectory control and/or warning features discussed abovewhen the vehicle is traveling in a forward direction with or without atrailer, and when the vehicle is traveling in a reverse direction withor without a trailer.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

What is claimed is:
 1. A method of controlling a speed of a motorvehicle and trailer, comprising: utilizing a controller to: determine adesired vehicle and trailer path while the vehicle is moving in reverseutilizing input from a rotatable knob inside the vehicle; and limit aspeed of a vehicle such that the vehicle does not exceed a maximumallowable speed for a measured trailer angle and moves along the desiredvehicle path within predefined error criteria.
 2. The method of claim 1,including: utilizing a steering command that is generated by a vehicle'sactive park assist system as an input to control a speed of a vehicle.3. The method of claim 1, including: limiting a speed of the vehicle toaccount for at least one of a maximum angular velocity of a powersteering system and a time lag of a power steering system.
 4. The methodof claim 1, including: controlling a path of a vehicle to avoid acollision; and generating a warning to a vehicle operator that acollision mitigation function is active.
 5. The method of claim 1,including: utilizing at least one of a vehicle brake system and atrailer brake system to limit vehicle speed in a reverse direction. 6.The method of claim 1, including: controlling a vehicle transmission tolimit vehicle speed.
 7. The method of claim 1, including: determining amaximum allowable vehicle speed in a reverse direction as a function ofat least one of a trailer angle and an input comprising a steeringcurvature command received from the rotatable knob; controlling at leastone of a braking system, an engine torque, and a transmission gearselection to prevent the motor vehicle from exceeding the maximumallowable vehicle speed.
 8. The method of claim 7, wherein: the maximumallowable vehicle speed is a linear function of the trailer angle. 9.The method of claim 7, including: determining a maximum allowablevehicle speed in a reverse direction as a function of both a trailerangle measured while the vehicle is moving in reverse and an inputcomprising a steering curvature command from the rotatable knob.